1. Field of the Invention
This invention relates generally to a method for determining the speed and direction of a rotating shaft, and more particularly a method using a rotor having teeth or gaps with unequal spacing.
2. Discussion of the Prior Art
Electronic controllers are provided on modern vehicles to monitor the operation of the vehicle and provide information to the engine, transmission, and other systems to control the functions thereof. One parameter which is monitored in several systems of the vehicles is the speed of rotating components. Some rotating components are provided in the transmission, driveline, and wheels.
Most prior art systems detect the speed of these components but often do not provide directional information. In such systems, a sensor detects the rotation of a rotating component. Typically, a rotor is provided with a plurality of evenly spaced teeth fixed to a rotating shaft. The rotor rotates with the shaft and a pickup sensor is placed in a position adjacent the rotor to sense the teeth as the rotor moves beneath the sensor. A controller is provided to receive a signal from the sensor. By counting the teeth and measuring time, the controller may calculate the speed of the shaft.
Additional sensors are required in most prior art systems to determine the direction of rotation of the component. In such a system, two sensors are placed in a particular spatial relationship with the teeth of the rotor. The sensors determine relative times at which an edge is detected. Thereafter, the controller may determine the direction of rotation. The additional sensor adds cost to the system and reduces reliability.
Another method for measuring direction of rotation is to provide a feature such as an oversized tooth, or, alternatively, delete a tooth on the rotor. Such a system is disclosed in U.S. Pat. No. 4,972,332, issued Nov. 20, 1992, to Luebbering et al ('332 patent). The apparatus in the '332 patent includes a rotor with such a feature. The '332 patent includes one undersized tooth surrounded by a standard size tooth, and two consecutive undersized teeth separated from the first undersized tooth by three standard sized teeth. The apparatus detects both the rising and falling edges of the teeth to determine speed and direction of the rotor. The direction of the rotor is determined by identifying the single undersized tooth.
When the apparatus of the '332 patent detects three standard sized teeth followed by two undersized teeth, a first direction is established. If the above sequence is not detected, the controller determines the shaft is rotating in the opposite direction. The apparatus of the '332 patent thus requires several teeth to rotate past the sensor before the rotational direction may be determined, and thus a relatively long time must pass before the direction is determined. Furthermore, because the method used in the '332 patent detects the edge of the teeth, a Hall Effect sensor must be used to accurately detect the edges of the tooth. A Hall Effect sensor is an active sensor, including an integrated circuit requiring a voltage input, and is a relatively complicated sensor. A Hall Effect sensor may have occasional reliability problems and is sensitive to temperature variation in its operating environment.
U.S. Pat. No. 5,371,460, issued Dec. 6, 1994, to Coffman et al, describes another system for measuring the speed and direction of rotation of a shaft. A rotor is provided in the '460 patent with pairs of teeth having different widths. The teeth of various width are spaced circumferentially about the rotor. As with the '332 patent, the '460 patent measures the edges of the teeth and determines the width of the tooth after detecting each edge of the tooth. The apparatus of the '460 patent then establishes the sequence of the teeth and determines in which direction the shaft is rotating. As with the '332 patent, the '460 patent requires a Hall Effect sensor to detect the edge of the teeth as described above. Furthermore, because the teeth are provided in pairs, the gaps between the teeth must also differ, otherwise the method taught in the '460 patent would be not functional, as an alternating wide and narrow tooth would be observed whether the shaft were rotating clockwise or counterclockwise.
It would be desirable to provide a method and apparatus for measuring the speed and direction of a rotating shaft using a simple sensor. It would also be desirable to provide such a method and apparatus having compensation for acceleration.